Some semiconductor manufacturing processes create a film on a semiconductor wafer by flowing a precursor onto the wafer and then activating a reaction of the substrate surface, usually with a plasma and/or second precursor. In one such process, atomic layer deposition (“ALD”), one or more vaporized precursors are flowed from an ampoule onto a semiconductor wafer as part of one or more “dose” steps during an ALD cycle. In some traditional semiconductor processing tools, some ways in which precursor is delivered to the processing chamber leads to precursor waste.